Project Summary: While currently available antiretroviral therapies are highly effective they are not curative. Patients are required to remain on life-long therapy which is associated with a variety adverse effects. Over time, viral-mediated drug resistance is likely to pose an increasingly serious problem for individuals on therapy. The development of novel classes of inhibitors that block viral replication differently from currently available drugs remains a high priority. Maturation inhibitors (MIs) represent one such class of HIV therapies. MIs block virus replication by disrupting the conversion of the capsid precursor protein, CA-SP1 (p25), to the mature form of capsid, CA (p24) resulting in the release of non-infectious viral particles. Unlike protease inhibitors that bind to and inhibit the action of the viral protease, MIs directly target the HIV-1 Gag protein. This novel mechanism of action allows MIs to retain full activity against viruses resistant to approved classes of HIV drugs. Clinical proof-of-concept for MIs was established with the first-in-class MI, bevirimat (BVM). In a series of trials, BVM was shown to be safe and effective in reducing HIV viral load in infected individuals, however, a lack of uniform patient response was also observed. Analysis of patient virus revealed that a single amino acid polymorphism in the SP1 region of the viral Gag protein was a primary determinant of patient response. This polymorphism involves a Val to Ala change at SP1 amino acid 7: V7A. Approximately 50% of HIV-1 isolates contain V7 and are highly sensitive to BVM while the remaining 50% contain A7 and lack sensitivity. DFH Pharma?s current efforts focus on the identification of next generation MIs with broad anti-HIV activity. Specifically, we have identified 2nd generation MIs that exhibit potent activity against the broad range of HIV isolates. Recent testing has determined that the most potent of these broadly active compounds exhibit IC50 values in the single digit nM range. This activity level is within the accepted range for HIV drug development candidates and compares favorably with MI clinical candidates. The goals of the work outlined in this application are to i) build on our phase I effort (1R41GM132683-01A1) to identify a 2nd gen MI development candidate to advance into IND-enabling studies and ii) initiate efforts to determine the potential for formulating MIs for delivery as long-acting agents. Importantly, this 2nd goal recognizes that the HIV treatment space is moving away from daily oral dosing towards formulations that support weekly, monthly or even less frequent drug application. Success in these efforts will result in a novel drug development candidate with long- acting formulation potential moving forward to IND-enabling studies.